1. Field of the Invention
This invention relates to a rotary switch device mounted e.g. in a tester (circuit tester) or the like as a range-switching device thereof and a tester incorporating the rotary switch device.
2. Prior Art
Conventionally, a rotary switch of the above-mentioned kind has been proposed e.g. by the present assignee in Japanese Utility Model Publication (Kokoku) No. 7-20824, in which a click mechanism is formed between a rotor having brushes mounted on its underside and a casing having the rotor fitted therein, while the rotor has its shaft rotatably fitted in a circuit board formed with electrical contacts, for being rotated by a dial, not shown in the publication, arranged on the top of the rotor. The click mechanism is constituted by a waved-surface portion constructed by crests and roots continuously formed along an inner peripheral surface of a circular opening of the casing and a click spring portion formed in a disk-shaped body of the rotor. When the dial covering the rotor is rotated, the click spring portion is rotated for clicking engagement with the waved-surface portion of the casing. The click spring portion is comprised of a pair of spring portions which mainly act as the springs and circular detent portions formed on ends of the respective spring portions. The click spring portion is formed by cutting the disk-shaped body of the rotor such that a portion having a generally crescent shape in plan view is removed therefrom.
The proposed rotary switch device having the above construction, however, has the problem that since the click spring portion is formed in a manner such that part of the disk-shaped body of the rotor is axially cut out to form a space which is crescent-shaped in plan view, a portion of the underside of the rotor for mounting the brushes becomes narrow. Inversely, if a large area is secured for the portion for mounting the brushes, the diameter of the rotor is required to be increased and hence the diameter of the dial covering the rotor is required to be made larger than required. Further, to impart the click spring portion a suitable spring force and at the same time prevent the same from having a useless or undesired twist, it is required that the click spring portion has a predetermined thickness, which results in an undesired increase in the thickness of the rotor per se and hence an undesired increase in the thickness of the whole rotary switch device.